Heating apparatus



July 5, .1938. L. WILSON HEATING APPARATUS Filed May 2, 1936 PatentedJuly 5, 1938 UNITED STATES PATENT OFFICE 2 Claims.

This invention relates to the art of heating and, particularly toindirect heating, e. g., that which is effected by passing hot fluidsthrough a conduit and by radiation from the latter to the point or v 5object to be heated.

that this problem is general and the applicability of the presentinvention is correspondingly broad. While the invention will bedescribed with particular reference to furnaces or annealing covers,this is merely by way of illustration and does not constitute alimitation upon the scope of the invention.

When it is attempted to heat a space or an object by passing hot fluidsthrough a radiating tube or conduit, the natural result is that thetemperature of the tube wall decreases progressively therealong from thepoint at which the hot gases are supplied thereto or generated therein.In other words, the hot fluids, such as combustion gases, cool graduallyas they 'give up heat to the tube. In many cases, however, it is desiredthat the temperature of the tube remain substantially constantthroughout its entire length, instead of presenting a so-called hot spotat the point of admission or generation of the-heating fluid, and aprogressively decreasing temperature from that point toward thedischarge end of the tube. This problem is particularly acute. in theprocess of annealing steel sheets in stacks, since the characteristicsof the finished product depend largely on the temperatures to .whichthey are heated during the annealing.

I have invented an apparatus whereby it is pos- 40 sible to obtain agreater uniformity in the temperatures at various'points along thelength of a radiant tube, even though the hot fluid supplying heatthereto is introduced or generated in a relatively confined spaceand-transmitted therealong, gradually losing heat to the tube. Inaccordance with my invention, I restrict the flow of heat radiallythrough the tube wall to varying degrees, the restriction being greatestadjacent the point of introduction or generation ofthe hotfluids, anddecreasing gradually along the length of the tube from thatpoint towardthe discharge end. I thus counteract the natural tendency for the tubeto radiate the, greater portion of the heat from the zone of its lengthtraversed by the gases while at their highest temperature, therestrictive effect being tapered 01!, along the length of the tube, topermit greater heat radiation from points at which the gases traversingthe tube are somewhat cooled from their original temperature.

My invention, in one embodiment, takes the 5 form of a plurality of;thickening bands disposed about the radiant tube at varying intervals.The bands are closest together at the points of introduction orgeneration of the hot fluid, the spacing therebetween increasinggradually toward the 1 discharge end of the tube. The thickening bandsprovide relatively short zones of' increased thickness and therebyrestrict transmission of heat radially of the tube wall.

For a complete understanding of the invention 15 reference is made tothe accompanying drawing illustrating several forms which the apparatusof my invention may take.

In the drawing:

Figure 1 is a view partly in section and partly in 20 elevation showinga radiant tube with thickening bands applied externally thereof;

' Fig. 2 is a view similar to Fig. 1 showing a modifled form;

Fig. 3 is a view similarto Fig. 1 showing .thick- 25 ening bandsdisposed interiorly of the tube; and

Fig. 4 is an axial section through a heating tube showing thickeningbands as illustrated in Fig.

,2 disposed interiorly of the radiant tube.

Referring now in detail to the drawing, aheat- 30 ing tube I0 isprovided at the end of a burner ll. Fuel and air for combustion aredelivered to the burner, by any known means (not shown). The resultingcombustion evolves considerable quantitles of hot gases in arelatively'short portion of 35 the tube length just beyond the burner.As the gases expand because of the heat generated, they flow along thetube toward the discharge end thereof indicated generally at II. Thefuel and air for combustion, of course, must be delivered 40 under apressure greater than that created in the tube by the expansion of ,thecombustion gases.

Thickening bands I! are disposed at intervals along the length of thetube III. In Fig. 1 these bands are simply annular rings and may be ofany desired shape or material and secured to the tubes in any convenientmanner. The dimension of the bands axially of the tube III is preferably50 several times (i. e., two or three times) the dimension thereofradially oi the tube. The bands II provide relatively short zones ofincreased thickness. This increased thickness, together with the film ofair or gas between the bands and the 55 tube, causes a reduction in theflow of heat radially of the tube wall, as compared to the rate of flowthrough the portions of the wall not covered by the bands.

The. spacing between the bands increases in proportion to the distancealong the tube from the burner II. As the hot gases travel along thetube and are cooled as a result of giving up heat thereto, a greaterproportion of tube surface uncovered by the thickening bands is providedto permit transmission of about the same amount of heat per unit lengthas in the tube sections nearer the burner. The temperature of the tubeat all points therealong is thus maintained substantially constant. Atthe discharge end, the entire surface of the tube may be left uncovered.

By this arrangement, I limit the amount of heat transmitted through thetube walls for radiation therefrom adjacent the burner where the minesthe temperatures of the tube at various points along its length. v

Figure 2 shows a slight modification in which the tube 10 is providedwith a helical wrapping of strip, wire, rod or the like, indicatedgenerally at l4.' The turns of the wrapping are spaced more closelyadjacent the burner II and at points remote therefrom, the spacingbetween turns increasing, gradually almost in proportion to the distancefrom the burner. The result produced by the structure shown in'Fig. 2 issubstantially the same as that of the arrangement of Fig. 1,

about the only difference being that the successive turns of thewrapping form helical bands which,

. instead of being independent, are connected each to its neighbors.

. Figure 3 illustrates a heating tube similar to that of Fig. 1 exceptthat the thickening bands I! are disposed interiorly of the tube insteadof exteriorly.

Figure 4 likewise shows a tube similar to that of Fig. 2 except that thehelical wrapping I4 is disposed inside the tube.

- It will be apparent from the foregoing description that the inventionmakes it possible to attain' a substantially uniform externaltemperature along all points of the heating tube despite the fact thatthe heating gases are hottest adjacent the burner and cooledprogressively as they flow therefrom along the tube. By properly spacingthe thickening bands, a considerable range of average external tubetemperatures may be obtained. The invention utilizes the principle thatthe average temperature along the outside of the tube is dependent uponthe heat transmitting characteristics of the wall section at variouspoints therealong.

While I have illustrated and described herein but pneembodiment of theinvention with certain modifications, it will be recognized that changesin the construction described may be made, within the scope of theappended claims,

without departing from the spirit of the. invention. In the claims, theterm bands is to be defined as including both the separate bands ofFigures 1 and 3 and the successive turns of a helix as shown in Figures2 and 4.

I claim:

1. In a heat exchange apparatus, a tube of substantially-uniform.diameter and wall thickness adapted to be heated by the passageof fluid therethrough, and thickening bands extending around the tube inspaced relation longitudinally thereof, the spacing between adjacentbands varying along the length of the tube, and the dimension of saidbands axially of the tube being several times their dimension radiallyof the tube.

2. In a heat, exchange apparatus, a tube of substantially uniformdiameter and wall thickness adapted to be heated by the passage of fluidtherethrough, and thickening bands extending around the tube in spacedrelation longitudinally thereof, the spacing between adjacent bandsvarying, along the length of the tube, the bands having a width greaterthan their thickness and disposed fiatwise on the tube.

